Shrinkage and Cracking in Cementitious Materials

Date This project started on 01 March 2013 and ended on 01 May 2016

Status This project is Finished

Authors
Eidgenössische Materialprüfungs- und Forschungsanstalt, CH
Technical University of Denmark, DK
Objectives

The objective of this project is to develop a fundamental understanding of the mechanisms leading to shrinkage cracking in cementitious materials through experimentation and development of reliable models.

The focus is on the impact of different binder compositions on free and restrained drying shrinkage.
When mortars are subjected to drying at early ages, moisture gradients develop between the drying surface and the inside of the specimen (gradients both of the local relative humidity and of the moisture content/degree of saturation).

As a consequence, the mortar will tend to shrink differently in the cross section and internal stresses will develop (partially consumed by stress relaxation), which might lead to cracks at the drying surface. In addition, the overall shrinkage of the mortar can lead to macrocracking in case of external restraint. The macroscopic cracking observed in the praxis and in laboratory tests (slabs, ring tests, linear restrained tests) is therefore the result of this complex interplay between external and internal restraint to volume changes, stress relaxation, surface cracking (crazing) and microcracking.

This project aims at linking micro-structural development to fundamental quantities believed to be key factors determining the risk of cracking: free shrinkage, strength, stiffness, fracture toughness and creep/relaxation. The analysis will directly take into account the variability of both shrinkage measurements and mechanical properties involved. The approach will allow assessing the effect of different types of blended cement on the risk of cracking.

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